1. Field of the Invention
The present invention relates to a chromatographic measurement apparatus that carries out measurement of an assay device using chromatography. In particular, the invention relates to a chromatographic measurement apparatus that tests a test article by measuring color development states of a test line, where a material that binds specifically to the test article is immobilized, and of a control line for determining the end of the measurement.
2. Description of the Related Art
In recent years, many assay devices have been developed, which are used to test a test article in simple and quick manner using an assay method, such as immunological measurement, where a sample (sample solution), which may possibly contain the test article, it fed onto a carrier. Now, various assay devices for testing extracorporeal diagnostic agents, toxic substances, etc., are commercially available. An example of such devices is one disclosed in U.S. Patent Application Publication No. 20080166821 (hereinafter, Patent Document 1), which uses immuno-chromatography. In the case where a device using immuno-chromatography is used, determination/measurement can be achieved in a simple manner without requiring a heavy equipment or machine, and the result of measurement can be obtained by putting the sample solution on the carrier and then leaving the carrier with the sample solution for as short as about 5 to 10 minutes, for example. Therefore, measurement techniques using an assay method, such as immunological measurement, are widely used as highly-specific, simple and quick measurement techniques in many situations, such as a clinical test at a hospital, a sample test at a laboratory, etc.
On the other hand, as a measurement apparatus for POCT (Point of Care Testing) for use at medical care sites, such as a doctor's office or a clinic, or at home, an immuno-chromatographic measurement apparatus (immuno-chromato-reader) is used for carrying out a test in a simple manner without need of a clinical test specialist. The immuno-chromatographic measurement apparatus allows highly sensitive measurement of a color development state of a reagent of a loaded device, and allows highly sensitive and highly reliable testing of the device even when the device is in a low color development state which is difficult to be observed and determined visually.
However, in order to carry out the test appropriately, it is necessary to wait for a reaction completion time (a time taken for the color development state of the test line to be visually observable after the sample solution is put on the device), which depends on the reagent (a material that binds specifically to the test article and being immobilized on the test line), after the sample solution is put on the device. This forces the user to measure the time after the sample solution is put on the device until the test result is obtained by the immuno-chromatographic measurement apparatus.
An immuno-chromatographic measurement apparatus disclosed in Japanese Unexamined Patent Publication No. 2009-133813 (hereinafter, Patent Document 2) carries out a testing process using data which is obtained by reading the color development state of the test line when a reaction completion time depending on the reagent has elapsed after the device is loaded. This apparatus carries out a preliminary testing process in the course of the measurement to determine a stage of progression of the reaction between the reagent and the test article injected in the device, and if it is determined that the reaction between the reagent and the test article has been completed, the last obtained result of the preliminary testing may be outputted as the final test result of this device. With this device, temporal change of the color development state and the test result can automatically be obtained after the sample solution is put on the device and until the end of the test, and time measurement by the user is not necessary. Therefore, the user can continue operation of putting the sample solution on other devices, etc.
The apparatus disclosed in Patent Document 2, however, is simple automation of the conventional method practiced by the user using a visual test kit (that is, in principle, determination of the test result is carried out when a reaction completion time determined for each reagent has elapsed; however, if it can be seen through visual observation that the reaction has apparently completed, the test result is determined before the reaction completion time elapses). Therefore, if the concentration of the test article in the sample solution is low or the reaction completion time determined for the reagent used is long, for example, it may take a considerably long time to obtain the test result. In particular, if the concentration of the test article in the sample solution is low, the color development state of the test line may not reach a predetermined value indicating a visually observable level, and an erroneous “negative (false-negative)” determination may be made.
In order to avoid such a situation, an amplifying solution may be put in advance on all the devices used in the test to amplify the color development state of the test line, or the amplifying solution may be put as appropriate depending on the state of progress of the test after a predetermined time to amplify the color development state of the test line and carry out the determination of the test result again. However, in the former case, the amplification step is carried out even when the test does not require the amplification step, and the time taken for obtaining the test result is increased. In addition, the amplifying solution is wasted. The latter case, after all, requires management and operation by the user for time measurement, and the user is interrupted by such operation.
As described above, although there are strong demands for a technique to provide a highly reliable test result in a simple and quick manner at the POCT sites, the conventional immuno-chromatographic measurement apparatuses have not succeeded in sufficiently responding to the demands.